Channel quality indicator for wireline channel degradation detection

ABSTRACT

Systems and techniques relating to channel degradation detection for communication systems are described. A described system includes a processor and an interface to transmit signals and receive signals via a channel that includes a cable. The processor can be configured to perform echo cancellation based on echo tap values to remove portions of the transmitted signals that appear as echoes within the received signals, signal equalization based on equalizer tap values, or both. The processor can be configured to determine a channel quality indicator of the channel based on one or more of the echo tap values, one or more of the equalizer tap values, or both. The processor can be configured to generate a warning indication based on the channel quality indicator indicating a degradation of the cable or the channel.

CROSS REFERENCE TO RELATED APPLICATIONS

This present disclosure is a continuation of and claims priority to U.S.application Ser. No. 15/380,965, filed on Dec. 15, 2016, which claimsthe benefit of the priority of U.S. Provisional Application Ser. No.62/268,073, filed Dec. 16, 2015, and entitled “DSP BASED CHANNEL QUALITYINDICATOR.” The above-identified applications are incorporated herein byreference in their entirety.

BACKGROUND

This disclosure relates to channel degradation detection forcommunication systems.

Communication systems can communicate over a wireline channel thatincludes a cable, connectors, and on-board components. Further, in somesystems, transmission and reception occur over the same cable includingthe same wire pair within the cable (e.g., as can occur in applicationsincluding half-duplex or full duplex communication systems). As such, acommunication system can use echo cancellation to remove echoes of atransmitted signal from a received signal. A communication system canuse equalization on a received signal to flatten a frequency response ofthe channel and remove time-domain Inter-Symbol Interference (ISI).

In some implementations, communication systems are based on the wirelineEthernet standard as defined by the Institute of Electrical andElectronics Engineers (IEEE) 802.3. In some implementations,communication systems are based on the IEEE 802.3bp standard(1000BASE-T1) for gigabit Ethernet over a single twisted pair forautomotive and industrial environments. In some implementations,communication systems are based on the IEEE 802.3bw standard(100BASE-T1) for 100 Mbit/s Ethernet over a single twisted pair forautomotive applications. In some implementations, Ethernet basedcommunication systems include a Physical Coding Sublayer (PCS) forauto-negotiation and low-level encoding; a Physical Medium Attachmentsublayer (PMA) for framing, octet synchronization, octet detection,scrambling, and descrambling; and a Physical Medium Dependent sublayer(PMD) that relates to the physical characteristics of signaltransmission and reception.

SUMMARY

The present disclosure includes systems and techniques for channeldegradation detection for communication systems. According to an aspectof the present disclosure, a system for channel degradation detectionincludes an interface to transmit signals and receive signals via achannel that includes a cable; an echo canceller coupled with theinterface, the echo canceller to perform echo cancellation based on echotap values to remove portions of the transmitted signals that appear asechoes within the received signals; an equalizer coupled with theinterface, the equalizer to perform signal equalization based onequalizer tap values, the equalizer tap values being determined based onat least a portion of the received signals to adjust an impulse responseof the channel and reduce inter-symbol interference within the receivedsignals; and circuitry configured to determine a return loss channelquality indicator of the channel based on the echo tap values, determinean insertion loss channel quality indicator of the channel based on theequalizer tap values, or both.

This and other implementations can include one or more of the followingfeatures. In some implementations, the circuitry is configured togenerate a warning indication based on the return loss channel qualityindicator or the insertion loss channel quality indicator exceeding athreshold, the warning indication indicating a degradation of the cableor the channel. In some implementations, the circuitry is configured todetermine the return loss channel quality indicator based on a summationof squared versions of the echo tap values. In some implementations, thecircuitry is configured to determine the return loss channel qualityindicator based on a summation of absolute value versions of the echotap values. In some implementations, the circuitry is configured todetermine the insertion loss channel quality indicator based on asummation of squared versions of the equalizer tap values. In someimplementations, the circuitry is configured to determine the insertionloss channel quality indicator based on a summation of absolute valueversions of the equalizer tap values. In some implementations, theequalizer includes a feedforward equalizer (FFE) and a decision-feedbackequalizer (DFE). In some implementations, the circuitry is configured toadjust channel compensation from the FFE before a determination of theinsertion loss channel quality indicator. In some implementations, theinsertion loss channel quality indicator is based on a main tap valueassociated with the DFE and a channel gain value. In someimplementations, the return loss channel quality indicator is mapped toa k-bit value, and wherein the insertion loss channel quality indicatoris mapped to a k-bit value.

The described systems and techniques can be implemented in electroniccircuitry, computer hardware, firmware, software, or in combinations ofthem, such as the structural means disclosed in this specification andstructural equivalents thereof. This can include at least onecomputer-readable medium embodying a program operable to cause one ormore data processing apparatus (e.g., a signal processing deviceincluding a programmable processor) to perform operations described.Thus, program implementations can be realized from a disclosed method,system, or apparatus, and apparatus implementations can be realized froma disclosed system, computer-readable medium, or method. Similarly,method implementations can be realized from a disclosed system,computer-readable medium, or apparatus, and system implementations canbe realized from a disclosed method, computer-readable medium, orapparatus.

For example, one or more disclosed embodiments can be implemented invarious systems and apparatus, including, but not limited to, a specialpurpose data processing apparatus (e.g., a remote environment monitor, arouter, a switch, a computer system component, a medium access unit), anautomotive communication system, a mobile computer, a digital camera, ageneral purpose data processing apparatus such as a computer, orcombinations of these.

Particular configurations of the technology described in this disclosurecan be implemented so as to realize one or more of the followingpotential advantages. A described technology can warn about potentialchannel degradation before the degradation impacts system performance. Adescribed technology can be implemented within low-cost systems,low-power systems, or both types of systems.

Details of one or more implementations are set forth in the accompanyingdrawings and the description below. Other features and advantages may beapparent from the description and drawings, and from the claims.

DRAWING DESCRIPTIONS

FIG. 1 shows a flowchart of an example of a process that includes echocancellation, equalization, and channel degradation detection based ontap values used for echo cancellation, equalization, or both.

FIG. 2 shows a block diagram of two communication devices coupled via awireline channel within a communication system.

FIG. 3 shows a block diagram of an example of a device that includes anecho canceller and equalizers.

FIG. 4 shows a flowchart of an example of a process that determines areturn loss channel quality indictor via echo cancellation.

FIG. 5 shows a flowchart of an example of a process that determines aninsertion loss channel quality indictor via channel equalization.

FIG. 6 shows a graph of an example of insertion loss channel qualityindicator estimation for different cable lengths.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

High speed communication is an important component in high-techautomotive applications, including cars and boats, and industrialsectors. With increased deployment of automotive Ethernet, advanced andsmarter diagnosis of the high speed communication system is beneficialfor system reliability. Further, automotive manufacturers and OriginalEquipment Manufacturers (OEMs) may require higher reliabilityperformance to deal with harsh environments for a communication channelsuch as those that exist within a car.

This disclosure presents techniques and systems to assess channelquality and warn about current or potential channel degradation thatimpacts or will impact reliability, throughput, or both. In someimplementations, a communication device, coupled with another device toform a wireline channel, computes a Channel Quality Indicator (CQI)which supplies reliability information about the channel. The CQI can beused for the diagnosis, maintenance, and service of the communicationsystem's reliability and aging issues. The channel can include one ormore cables, connectors, and on-board components. The device can computea CQI of Insertion Loss (IL-CQI), a CQI of Return Loss (RL-CQI), orboth. The insertion loss reflects channel attenuation and ISI. Thereturn loss reflects echoes of a transmitted signal within receivedsignals. Channel degradation, over time, typically increases insertionloss, return loss, or both. In some implementations, a device usescircuitry such as a processor, e.g., a digital signal processor (DSP),to compute CQIs such as IL-CQI, RL-CQI or both. In some implementations,a device uses circuitry such as an application-specific integratedcircuit (ASIC) or specialized logic device(s) to compute CQIs. TheseCQI-based solutions can be readily used in IEEE Ethernet standards suchas 802.3bp and 802.3bw. Further, in the automotive maintenance andsystem auto-diagnosis, the requirement for system aging and failureprediction is important for automotive safety and failure diagnosis atservice time. Also, simple implementation and less computing power aredesign factors for supporting a wide range of applications.

FIG. 1 shows a flowchart of an example of a process that includes echocancellation, equalization, and channel degradation detection based ontap values used for echo cancellation, equalization, or both. At 110,the process transmits and receives signals between devices coupled by achannel that includes a cable. For example, a controller device canrequest data from a sensor device or send a command to another device tocause an action to occur, e.g., start engine. In some implementations,the process operates a transceiver to transmit and receive signals. At115, the process performs echo cancellation based on echo tap values toremove portions of the transmitted signals that appear as echoes withinthe received signals. In some implementations, the transmitted signalsare provided to an echo canceller which is configured to store the lastN signal values and apply N echo tap values respectively to the storedsignal values to generate an output signal that reduces or eliminatesechoes within the received signals.

At 120, the process performs equalization based on equalizer tap valuesto adjust the channel's impulse response and reduce inter-symbolinterference within the received signals. The process can use one ormore equalizers such as a feedforward equalizer (FFE) or adecision-feedback equalizer (DFE). In some implementations, theequalizers are located after echo cancellation, and accordingly, operateon an echo cancelled version of a received signal. In someimplementations, an equalizer is configured to store M signal valuesthat represent currently or previously received signal values. In someimplementations, an equalizer is configured to store M signal valuesthat represent the output values of a slicer that makes a decision as towhether a portion of a received signal represents a one or a zero. Insome implementations, the process uses an adaptation technique such as aLeast-Mean-Square (LMS) technique to determine the equalizer tap values.In some implementations, the process causes the devices to exchange atraining sequence in order to measure ISI within the channel. In someimplementations, the process executes the training sequence, adaptation,or both at predetermined intervals.

At 125, the process determines a CQI, e.g., RL-CQI, IL-CQI, or both,based on tap values such as the echo tap values, equalizer tap values,or both. An example of a process for determining a CQI based on echo tapvalues is described in connection with FIG. 4. An example of a processfor determining a CQI based on equalizer tap values is described inconnection with FIG. 5. At 130, the process determines whether the CQIexceeds a threshold. In some implementations, the process uses athreshold that is set based on a dB increase, e.g., 1 dB, 2 dB, or 3 dB,over an initial calibration value such as a RL-CQI or IL-CQI that isdetermined when the channel is not degraded, e.g., at or around the timeof manufacture. In some implementations, the process uses a thresholdthat is set based on a predetermined value, which can be determinedbefore manufacture.

If exceeded, the process at 140 a, produces a warning indication toindicate cable or other channel degradation. The warning indication cantrigger a user interface warning, e.g., a check system light akin to acar's check engine light. If not exceeded, the process at 140 b,produces a normal indication to indicate that the channel is withinnormal operating parameters. In some implementations, a normalindication either maintains a check system light in the off-state orturns off the light. In some implementations, an application programminginterface (API) can be used to provide access to channel quality andwarning information.

FIG. 2 shows a block diagram of two communication devices 205 a, 205 bcoupled via a wireline channel 220 within a communication system. Thedevices 205 a-b include processor electronics 210 such as one or moreprocessors that implement methods effecting the techniques presented inthis disclosure. Each of the devices 205 a-b includes a memory 225configured to store information such as data, instructions, or both. Insome implementations, the memory 225 includes instructions for processorelectronics 210, DSP 240, or both. The devices 205 a-b includetransceiver electronics 215 to transmit and receive signals over a cablewithin the channel 220. In some implementations, the channel 220includes multiple wire pairs.

In this example, signal transmission and reception occur on the samewires, and accordingly, echoes of transmitted signals can appear inreceived signals. The transceiver electronics 215 includes a DSP 240configured to perform echo cancellation 244 to remove echoes of atransmitted signal that appear within received signals. The DSP 240 isfurther configured to perform channel equalization 242 on signalsreceived over the channel 220. In some implementations, the DSP 240determines an IL-CQI 246 based on coefficients used for channelequalization 242. In some implementations, the DSP 240 determines aRL-CQI 248 based on coefficients used for echo cancellation 244. Achannel degradation detector 250 compares the IL-CQI value and RL-CQIvalue to respective IL and RL thresholds. If any of the values exceedtheir respective thresholds, the channel degradation detector 250 cantrigger a warning, such as activating a car's service required light orsending a service required message to a server. In some implementations,processor electronics 210 are configured to perform the actions of thechannel degradation detector 250. In some implementations, processorelectronics 210 forward information from the channel degradationdetector 250 to a vehicle's On-Board Diagnostic (OBD) system.

FIG. 3 shows a block diagram of an example of a device 301 that includesan echo canceller 390 and equalizers 350, 355. A transmit pathway of thedevice 301 includes a digital-to-analog converter (DAC) 305, transmit(TX) power spectral density (PSD) filter 310, forward error correction(FEC) encoder 315, and a Physical Coding Sublayer (PCS) encoder 320. Areceive pathway of the device 301 includes an analog-to-digitalconvertor (ADC) 330, digital timing recovery 335, echo canceller 390,summer 340, feedforward equalizer (FFE) 350, gain (G) determination 345,DC (direct current) offset correction 347, decision-feedback equalizer(DFE) 355, slicer 360, FEC decoder 365, PCS decoder 370, adaptationengine 380, and PMA control 385. In some implementations, the device 301is coupled with or includes a channel degradation detector 395. Thedevice 301 performs echo cancellation via echo canceller 390 and summer340.

The device 301 includes components such as echo canceller 390 and summer340 to provide compensation for echoes within the channel. Theadaptation engine 380 can determine echo tap values for the echocanceller 390. The echo canceller 390 uses the echo tap values andtransmit values from the FEC encoder 315 on the transmit path to producea cancellation signal. A negated version of the cancellation signal issummed via summer 340 with the sampled signal produced by the ADC 330.

The echo tap values used by the echo canceller 390 reflect the returnloss magnitude. A channel degradation detector 395 can map echo tapvalues into a RL-CQI. The power of the time domain reflection is equalto the total frequency return loss power. Hence, RL-CQI determinationcan be performed in either the time or frequency domain. By calculatinga sum of echo tap power values or a sum of absolute values of the echotaps, the device 301 can estimate the RL-CQI and the receiver dynamicrange by one or more reflections, e.g., echoes, caused by one or morechannel components, e.g., cable, connectors, in a system containing thedevice 301. In some implementations, information such as the RL-CQI isused to evaluate how much margin is left for the system to operatecorrectly in different environments.

The device 301 includes components such as FFE 350, DFE 355, and gaindetermination 345 to provide compensation for the channel's insertionloss. The echo cancelled signal is provided to the FFE 350 and gaindetermination 345. Further, the device 301 corrects the DC offset via DCoffset correction 347 before the signal is provided to the slicer 360.In some implementations, a Narrowband Interference (NBI) noisecancellation block includes the FFE 350 and the DFE 355. The DFE 355operates on the output of the slicer 360 and produces a signal that issummed with the output of DC offset correction 347. The adaptationengine 380 can determine tap values for the FFE 350 and the DFE 355 viaan adaptation technique such as LMS. Other techniques are possible. TheFFE 350 tap values can include one or more precursor values, a main tap,and one or more post-cursor values. The DFE 355 tap values can includeone or more post-cursor values.

The channel degradation detector 395 can map equalizer tap values usedby an equalizer 350, 355 into an IL-CQI. While the number of taps forthe equalizers 350, 355 can be increased to provide additionalcompensation, a corresponding increase in computing power is typicallyrequired to perform equalization and determine equalizer coefficients.However, such increased computing power may not be available for lowpower or low cost systems. Thus, when channel components begin todegrade, a low power or a low cost system may not be able to fullycompensate for the degradation.

The integral of signal power in the time domain is equal to the integralof signal power in the frequency domain. When there is no insertionloss, only the main tap of the FFE 350 is required, the gain is zero,and the DFE 355 tap values are zeros. When the ideal signal passesthrough the channel to device 301, the channel's output includes theattenuated main tap and inter-symbol interference. If the tap values ofthe FFE 350, except for the main tap, are forced zeros and the channelis equalized by DFE 350 and gain determination 345, the signal power inthe time domain is the gain G times the sum of the main tap power andthe DFE tap power (e.g., ISI power). ISI power itself reflects thecondition of the channel. In order to be correctly equalized by the DFE355, the precursors of the FFE 350 and a few post-cursors of the FFE 350may be required to establish good equalization by the DFE 355.

In some implementations, data symbols are converted into one-channelPAM3 symbols (a form of pulse amplitude modulation) at 750M symbols persecond. A Digital Timing Loop (DTL) of the device 301 includes digitaltiming recovery 335 to control the sampling phase of the ADC 330 basedon the data error.

FIG. 4 shows a flowchart of an example of a process that determines areturn loss channel quality indictor via echo cancellation. At 401, theprocess transmits a signal via a wireline channel. At 405, the processstores transmit signal values in registers for use as delayed echovalues. In some implementations, the stored values reflect pre-filteredversions of the transmit signals.

At 410, the process receives signals via the wireline channel. In thisexample, transmitting and receiving signals occur via the same cablewithin the wireline channel. Echo triggers, such as impedance mismatchesand aging of channel components, cause echoes to occur reflecting adevice's transmitted signal back into the device's received signal. Insome implementations, transmitting and receiving signals are based onnominal packet exchanges between devices within a system. In someimplementations, a packet exchange includes a training sequence used todetermine the echo characteristics of the channel.

At 415, the process uses an adaption technique to determine echo tapvalues based on respective echoes of the transmitted signal as detectedwithin the received signals. The echo tap values can be adapted to makethe residue after the echo cancellation minimum. In someimplementations, the number of echo tap values is determined by themaximum cable length.

At 420, the process performs echo cancellation based on the echo tapvalues and the delayed echo values. In some implementations, the processperforms echo cancellation based on:

$E = {\sum\limits_{i = 1}^{p}{{echo}_{i}D^{i}}}$where p represents the number of echo taps within an echo canceller,echo_(i) represents the i^(th) echo tap value which corresponds to thei^(th) echo magnitude, and D^(i) represents the i^(th) delayed echovalue. Ideally, if there are no echoes, all the echo tap values would bezero. However, since echoes occur and may worsen over time as channelcomponents such as a cable deteriorate, the echo tap values are orbecome non-zero.

At 425, the process determines a RL-CQI based on the echo tap values,e.g., sum of squared tap values, sum of absolute tap values, etc. Insome implementations, the RL-CQI is expressed asRL _(CQI)=echo₁ ²+ . . . +echo_(p) ².In some implementations, the RL-CQI is expressed asRL _(CQI)=|echo₁|+ . . . +|echo_(p)|.Other expressions for RL-CQI are possible. In some implementations,RL-CQI determination at 425 is performed at periodic intervals, whereasecho cancellation at 420 is continuous insofar as there is a continuousstream of transmitted signals to cancel. In some implementations, theRL-CQI is quantized and mapped to a k-bit value, such as a 4-bit value,however other values for high dynamic range or high precision arepossible.

FIG. 5 shows a flowchart of an example of a process that determines aninsertion loss channel quality indictor via channel equalization. At510, the process receives signals via a wireline channel. In someimplementations, the signals include training symbols that are used fordetermining equalizer tap values. At 520, the process uses an adaptationtechnique such as LMS to determine equalizer tap values, such as FFE tapvalues, DFE tap values, or both, based on at least a portion of thereceived signals to adjust an impulse response of the channel and reduceinter-symbol interference within the received signals. In someimplementations, the process performs echo cancellation on the receivedsignals before determining equalizer tap values.

At 525, the process configures one or more equalizers based on theequalizer tap values. In some implementations, the process loads the tapvalues into an equalizer's tap registers. In some implementations, theprocess performs FFE based on the following equation:

$\sum\limits_{i = {- m}}^{n}{w_{i}D^{i}}$where w_(i) represents the i^(th) FFE tap value, D^(i) represents thei^(th) delay value, index values of [−m, −l] correspond to precursorvalues, [l, n] represent post-cursor values, and 0 is the main tapvalue. In some implementations, the process retrieves the delay valuesfor FFE from a bank of registers that store received signal values. Insome implementations, the process performs DFE based on the followingequation:

$\sum\limits_{i = 1}^{l}{f_{i}D^{i}}$where f_(i) represents the i^(th) DFE tap value, D^(i) represents thei^(th) delay value, and l is the number of DFE taps. In someimplementations, the process retrieves the delay values for DFE from abank of registers that store the output values of a slicer, e.g., seeslicer 360 of FIG. 3, that makes bit decisions based on an input and adecision threshold. In some implementations, the number of FFE and DFEtaps is determined by the cable insertion loss.

At 530, the process determines an IL-CQI based on the equalizer tapvalues and a gain value. The process can determine an IL-CQI based on atechnique such as a sum of squared tap values or a sum of absolute tapvalues. In some implementations, the IL-CQI is expressed as any one ofthe following:IL _(CQI) =G×(1+f ₁ ² + . . . +f _(l) ²)IL _(CQI) =G×(f ₁ ² + . . . +f _(l) ²)IL _(CQI) =G×(1+|f ₁ |+ . . . +|f _(l)|)where G represents a gain. The gain can reflect a signal attenuationwithin the channel. Note that non-zero values of precursor orpost-cursor FFE taps may induce an estimation error, but the precursorpower can be neglected. In some implementations, the process calculatesthe normalized and relative power, and the post-cursor power of the FFEcan be ignored for the channel quality comparison once calibrated. Insome implementations, the main tap of the DFE is used for a real-timeIL-CQI determination as follows: IL_(CQI)=G×1. In some implementations,IL-CQI determination includes adjusting, e.g., shaping or limiting, theFFE compensation and using DFE, main tap, and G to estimate the IL ofthe channel. In some implementations, the IL-CQI is quantized and mappedto an k-bit value, such as a 4-bit value, however other values for n arepossible. In some implementations, the process computes IL_(CQI)=G×1after the startup training is performed, and the process computesIL_(CQI)=G×(1+f₁ ²+ . . . +f_(l) ²) in a stage of startup training or ina test mode.

FIG. 6 shows a graph of an example of insertion loss channel qualityindicator estimation for different cable lengths. The graph 601 plots dBvalues corresponding to IL_(CQI)=G×(1+f₁ ²+ . . . +f_(l) ²) for a rangeof cable lengths. The graph 601 reflects an increase in channelattenuation based on an increase in cable length. While thedetermination of the IL-CQI is agnostic to cable length, a calibrationprocess can determine a base-line threshold for a nominal IL-CQI when asystem is initially manufactured. In some implementations, when theIL-CQI exceeds a predetermined percentage of the base-line threshold(e.g., 1 dB, 2 dB, 3 dB, etc.) then a channel degradation detectorindicates a warning.

In some implementations, a technique includes transmitting signals via achannel that includes a cable; receiving signals via the channel;performing echo cancellation based on echo tap values to remove portionsof the transmitted signals that appear as echoes within the receivedsignals; determining equalizer tap values based on at least a portion ofthe received signals to adjust an impulse response of the channel andreduce inter-symbol interference within the received signals; performingsignal equalization based on the equalizer tap values; and determining achannel quality indicator of the channel. In some implementations,determining the channel quality indicator includes determining a returnloss channel quality indicator of the channel based on the echo tapvalues, determining an insertion loss channel quality indicator of thechannel based on the equalizer tap values, or both.

The technique can include generating a warning indication based on thereturn loss channel quality indicator or the insertion loss channelquality indicator exceeding a threshold, the warning indicationindicating a degradation of the cable or the channel. The technique caninclude determining the return loss channel quality indicator based on asummation of squared versions of the echo tap values. The technique caninclude determining the return loss channel quality indicator based on asummation of absolute value versions of the echo tap values. Thetechnique can include determining the insertion loss channel qualityindicator based on a summation of squared versions of the equalizer tapvalues. The technique can include determining the insertion loss channelquality indicator based on a summation of absolute value versions of theequalizer tap values. Performing the signal equalization can includeusing a FFE and a DFE. The technique can include adjusting channelcompensation from the FFE before a determination of the insertion losschannel quality indicator. In some implementations, the insertion losschannel quality indicator is based on a main tap value associated withthe DFE and a channel gain value. In some implementations, the returnloss channel quality indicator is mapped to a k-bit value. In someimplementations, the insertion loss channel quality indicator is mappedto a k-bit value.

In some implementations, a communication system includes multipledevices include a first device and a second device communicativelycoupled with the first device via a channel that includes a cable. Oneor more of these devices can include an interface to transmit signalsand receive signals via the channel and a processor. The processor canbe configured to perform echo cancellation based on echo tap values toremove portions of the transmitted signals that appear as echoes withinthe received signals, determine equalizer tap values based on at least aportion of the received signals to adjust an impulse response of thechannel and reduce inter-symbol interference within the receivedsignals, perform signal equalization based on the equalizer tap values,and determine a return loss channel quality indicator of the channelbased on the echo tap values, determine an insertion loss channelquality indicator of the channel based on the equalizer tap values, orboth. The system can include circuitry to generate a warning indicationbased on the return loss channel quality indicator or the insertion losschannel quality indicator exceeding a threshold, the warning indicationindicating a degradation of the cable or the channel. In someimplementations, the processor is configured to determine the returnloss channel quality indicator based on a summation of squared versionsof the echo tap values or a summation of absolute value versions of theecho tap values. In some implementations, the processor is configured todetermine the insertion loss channel quality indicator based on asummation of squared versions of the equalizer tap values or a summationof absolute value versions of the equalizer tap values.

A few embodiments have been described in detail above, and variousmodifications are possible. The disclosed subject matter, including thefunctional operations described in this specification, can beimplemented in electronic circuitry, computer hardware, firmware,software, or in combinations of them, such as the structural meansdisclosed in this specification and structural equivalents thereof,including potentially a program operable to cause one or more dataprocessing apparatus to perform the operations described (such as aprogram encoded in a computer-readable medium, which can be a memorydevice, a storage device, a machine-readable storage substrate, or otherphysical, machine-readable medium, or a combination of one or more ofthem).

The term “data processing apparatus” encompasses all apparatus, devices,and machines for processing data, including by way of example aprogrammable processor, a computer, or multiple processors or computers.The apparatus can include, in addition to hardware, code that creates anexecution environment for the computer program in question, e.g., codethat constitutes processor firmware, a protocol stack, a databasemanagement system, an operating system, or a combination of one or moreof them.

A program (also known as a computer program, software, softwareapplication, script, or code) can be written in any form of programminglanguage, including compiled or interpreted languages, or declarative orprocedural languages, and it can be deployed in any form, including as astand alone program or as a module, component, subroutine, or other unitsuitable for use in a computing environment. A program does notnecessarily correspond to a file in a file system. A program can bestored in a portion of a file that holds other programs or data (e.g.,one or more scripts stored in a markup language document), in a singlefile dedicated to the program in question, or in multiple coordinatedfiles (e.g., files that store one or more modules, sub programs, orportions of code). A program can be deployed to be executed on onecomputer or on multiple computers that are located at one site ordistributed across multiple sites and interconnected by a communicationnetwork.

While this specification contains many specifics, these should not beconstrued as limitations on the scope of what may be claimed, but ratheras descriptions of features that may be specific to particularembodiments. Certain features that are described in this specificationin the context of separate embodiments can also be implemented incombination in a single embodiment. Conversely, various features thatare described in the context of a single embodiment can also beimplemented in multiple embodiments separately or in any suitablesubcombination. Moreover, although features may be described above asacting in certain combinations and even initially claimed as such, oneor more features from a claimed combination can in some cases be excisedfrom the combination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. In certain circumstances, multitasking and parallel processingmay be advantageous. Moreover, the separation of various systemcomponents in the embodiments described above should not be understoodas requiring such separation in all embodiments.

What is claimed is:
 1. An apparatus comprising: an interface to transmitsignals and receive signals via a channel that includes a cable; and aprocessor coupled with the interface, wherein the processor isconfigured to perform i) echo cancellation based on echo tap values toremove portions of the transmitted signals that appear as echoes withinthe received signals, ii) signal equalization based on equalizer tapvalues, the equalizer tap values being determined based on at least aportion of the received signals to adjust an impulse response of thechannel and reduce inter-symbol interference within the receivedsignals, or iii) both the echo cancellation and the signal equalization,wherein the processor is configured to determine a channel qualityindicator of the channel based on one or more of the echo tap values,one or more of the equalizer tap values, or both one or more of the echotap values and one or more of the equalizer tap values, and wherein theprocessor is configured to generate a warning indication based on thechannel quality indicator indicating a degradation of the cable or thechannel.
 2. The apparatus of claim 1, wherein the channel qualityindicator comprises a return loss channel quality indicator of thechannel that is based on one or more of the echo tap values, aninsertion loss channel quality indicator of the channel that is based onone or more of the equalizer tap values, or both the return loss channelquality indicator and the insertion loss channel quality indicator. 3.The apparatus of claim 2, wherein the processor is configured togenerate the warning indication based on the return loss channel qualityindicator exceeding a first threshold, the insertion loss channelquality indicator exceeding a second threshold, or both.
 4. Theapparatus of claim 2, wherein the processor is configured to determinethe return loss channel quality indicator based on a summation ofabsolute value versions or squared versions of the echo tap values. 5.The apparatus of claim 2, wherein the processor is configured todetermine the insertion loss channel quality indicator based on asummation of absolute value versions or squared versions of theequalizer tap values.
 6. The apparatus of claim 2, wherein the returnloss channel quality indicator is mapped to a k-bit value, and whereinthe insertion loss channel quality indicator is mapped to a k-bit value.7. The apparatus of claim 1, wherein the channel quality indicatorcomprises an insertion loss channel quality indicator of the channelthat is based on one or more of the equalizer tap values, wherein theprocessor is configured to perform the signal equalization, wherein thesignal equalization comprises feedforward equalization anddecision-feedback equalization, and wherein the processor is configuredto adjust channel compensation from the feedforward equalization beforea determination of the insertion loss channel quality indicator.
 8. Theapparatus of claim 7, wherein the insertion loss channel qualityindicator is based on a main tap value associated with thedecision-feedback equalization and a channel gain value.
 9. A methodcomprising: transmitting signals via a channel that includes a cable;receiving signals via the channel; performing i) echo cancellation basedon echo tap values to remove portions of the transmitted signals thatappear as echoes within the received signals, ii) signal equalizationbased on equalizer tap values, the equalizer tap values being determinedbased on at least a portion of the received signals to adjust an impulseresponse of the channel and reduce inter-symbol interference within thereceived signals, or iii) both the echo cancellation and the signalequalization; determining a channel quality indicator of the channelbased on one or more of the echo tap values, one or more of theequalizer tap values, or both one or more of the echo tap values and oneor more of the equalizer tap values; and generating a warning indicationbased on the channel quality indicator indicating a degradation of thecable or the channel.
 10. The method of claim 9, wherein determining thechannel quality indicator comprises determining a return loss channelquality indicator of the channel based on one or more of the echo tapvalues, determining an insertion loss channel quality indicator of thechannel based on one or more of the equalizer tap values, or both. 11.The method of claim 10, wherein generating the warning indicationcomprises generating the warning indication based on the return losschannel quality indicator exceeding a first threshold, the insertionloss channel quality indicator exceeding a second threshold, or both.12. The method of claim 10, wherein determining the return loss channelquality indicator comprises determining the return loss channel qualityindicator based on a summation of absolute value versions or squaredversions of the echo tap values.
 13. The method of claim 10, whereindetermining the insertion loss channel quality indicator comprisesdetermining the insertion loss channel quality indicator based on asummation of absolute value versions or squared versions of theequalizer tap values.
 14. The method of claim 9, wherein determining thechannel quality indicator comprises determining an insertion losschannel quality indicator of the channel based on one or more of theequalizer tap values, wherein the signal equalization comprisesfeedforward equalization and decision-feedback equalization, and whereinthe method comprises adjusting channel compensation from the feedforwardequalization before a determination of the insertion loss channelquality indicator.
 15. The method of claim 14, wherein the insertionloss channel quality indicator is based on a main tap value associatedwith the decision-feedback equalization and a channel gain value.
 16. Asystem comprising: a first device of a car, the first device comprisingan interface to transmit signals and receive signals via a channel thatincludes a cable that is subjected to an automotive environment of thecar, and a processor coupled with the interface; and a second device ofthe car, the second device being communicatively coupled with the firstdevice via the cable, wherein the processor is configured to perform i)echo cancellation based on echo tap values to remove portions of thetransmitted signals that appear as echoes within the received signals,ii) signal equalization based on equalizer tap values, the equalizer tapvalues being determined based on at least a portion of the receivedsignals to adjust an impulse response of the channel and reduceinter-symbol interference within the received signals, or iii) both theecho cancellation and the signal equalization, wherein the processor isconfigured to determine a channel quality indicator of the channel basedon one or more of the echo tap values, one or more of the equalizer tapvalues, or both one or more of the echo tap values and one or more ofthe equalizer tap values, and wherein the processor is configured todetect a degradation of the cable or the channel over time resultingfrom being subjected to the automotive environment of the car based onthe channel quality indicator.
 17. The system of claim 16, wherein thechannel quality indicator comprises a return loss channel qualityindicator of the channel that is based on one or more of the echo tapvalues, an insertion loss channel quality indicator of the channel thatis based on one or more of the equalizer tap values, or both the returnloss channel quality indicator and the insertion loss channel qualityindicator.
 18. The system of claim 17, wherein the processor isconfigured to determine the return loss channel quality indicator basedon a summation of absolute or squared versions of the echo tap values,and wherein the processor is configured to determine the insertion losschannel quality indicator based on a summation of absolute or squaredversions of the equalizer tap values.
 19. The system of claim 17,wherein the processor is configured to generate a warning indicationbased on the return loss channel quality indicator exceeding a firstthreshold, the insertion loss channel quality indicator exceeding asecond threshold, or both.
 20. The system of claim 19, comprising:on-board diagnostic system of the car, wherein the first device isconfigured to forward the return loss channel quality indicator to theon-board diagnostic system, forward the insertion loss channel qualityindicator to the on-board diagnostic system, or both.